The invention relates to a method and apparatus for generating pulse sequences gaplessly following each other.
More particularly, the practice of the invention provides pulses of precise time and accurately displaced in time.
Such pulse sequences are particularly needed for, inter alia, testing storage products (storages with associated buffers), test systems, data processing systems, and communication systems.
When storage products are tested a corresponding pulse pattern is applied thereto. The reaction of the storage product on this pulse pattern is recorded, and compared with theoretical nominal values. The comparison of both values permits a conclusion as to whether the storage product operates as required, or whether there are errors at specific locations.
The pulse sequence to be generated is initially determined theoretically by the specifications of the storage product. On the basis of these theoretical values the pulses required are generated by a pulse generator.
Formerly, a storage product was tested with a hardware testing device specifically designed for the product. However, the disadvantage of such hardware testing devices is that they can only be used for a specific storage product.
Another disadvantage is that there are so-called waiting periods during which the product to be tested can undergo specific alterations, e.g. discharge or recharge of capacities, etc.
It is to be appreciated for a better understanding of the invention that there are testing requirements where upon an occurrence determined by the product, one pulse sequence has to be followed by another one, i.e. the original pulse sequence is to be replaced by a new pulse sequence upon such an occurrence. The switching from one pulse sequence to another one required a predetermined time interval in conventional hardware testing devices. A gapless switching has not been possible with prior art devices since the switching to a new pulse sequence can only be effected subsequent in time to the fading of the electrical transients due to switching. The effect of the required waiting period, however, was that during this waiting period new conditions could appear in the product to be tested.
In U.S. Pat. No. 4,203,543 the applicant disclosed a method and apparatus for generating pulse cycles gaplessly, one following the other. The Abstract of U.S. Pat. No. 4,203,543 reads as follows:
"This discloses a pattern generator having a programmable product cycle timer in which a pulse train, i.e., the pattern generated can be repeated or switched from a first pulse frequency to a second pulse frequency without the usual transient switching periods between pulses. The invention accomplishes this by providing the generator with a cycle timer using a clock operating in conjunction with a down counter so that at a preselected time interval, before the end of the pulse is achieved, a test is made to determine if a required condition needing a different pulse frequency exists. If such a condition does not exist the present pulse frequency is reinitiated so that at count 0 it is repeated without delay. If the required condition does exist loading of the needed pulse frequency is initiated so that upon termination of the presently existing pulse at count 0, the newly selected pulse will be introduced into the product being tested without delay". PA1 "This discloses a pattern generator having a programmable product cycle timer in which a pulse train, i.e., the pattern generated, having a time raster measurable to one nanosecond can be repeated or switched from a first pulse frequency to a second pulse frequency without the usual transient switching periods between pulses. The invention accomplishes this by providing the generator with a cycle timer using a ten nanosecond clock operating in conjunction with a ten nanosecond down counter so that a pre-selected time interval, before the end of the pulse is achieved, a test is made to determine if a required condition needing a different pulse frequency exists. If such a condition does not exist the present pulse frequency is reinitiated so that at count 0 it is repeated without delay. If the required condition does exist loading of the needed pulse frequency is initiated so that upon termination of the presently existing pulse at count 0, the newly selected pulse will be introduced into the product being tested without delay. A programmable cycle timer is provided to permit the implementation of pulses which has a time raster that is other than a ten nanosecond multiple". PA1 "A digitally programmable electronic delay may be achieved by counting pulses of a stable clock and providing an output signal when a prescribed count is reached. This is done with a synchronous counter and an Exclusive OR matching circuit. The resolution of this delay is limited by the smallest clock period that can be counted, a speed limit of the logic blocks used. Two programmable delays with different clock periods are employed such that a total delay of any combination of the two periods can be programmed. The smallest interval being the difference between the two periods. One of the clocks is a stable reference and the other is controllable. Both clock rates are divided down to a common frequency and these signals are compared in a phase detector. The output of the phase detector is fed back to the controllable clock so that the relative time position of the two clocks is held constant. The Electronic delay apparatus or timer employs a Read Only Memory (ROM) for selecting the time interval or delay. For example, in the illustrative embodiment set forth in detail hereinafter, a pulse may be delayed any integer number of nanoseconds. Correspondingly, a pulse may be provided at any integer number of nanoseconds with respect to a reference time. When the digital input word is increased, each counter produces an output at the time when the value of the counter (clock periods of delay) is equal to the respective binary data programmed into it. This will cause T delay to increase relative to T reference. T delay then, will be equal to the number of T.sub.1 clock periods plus the number of T.sub.2 clock periods added together. T reference will repeat every cycle at the same point in time, regardless of the programmed delay value."
In U.S. Pat. No. 4,263,669 the applicant discloses a method and apparatus for generating pulse cycles gaplessly, one following the other. The Abstract of U.S. Pat. No. 4,263,669 reads as follows:
Referring to U.S. Pat. No. 4,263,669, it is possible to provide pulse intervals in the 1 nanosecond time raster. However, the beginning of a new pulse interval has to be in accordance with the beginning of a 10 nanosecond time raster derived from a quartz oscillator. For that reason, there occurs so-called "dead times" of approximately 20 ns which appeared either before the start of a pulse to be newly generated, or after the decay of an already generated pulse, up to the beginning of the following pulse interval. This is due to the fact that the 1 nanosecond delay values for the pulses to be generated to control the circuit have to be loaded into corresponding counters, and that these loading processes can be executed only while there was no pulse generation, or after the decay of a generated pulse. It was thus not possible to provide pulse intervals following each other with a time resolution in the 1 nanosecond time raster.
Reference is made to U.S. Pat. No. 3,913,021 entitled "High Resolution Digitally Programmable Electronic Delay For Multi-Channel Operation" granted Oct. 14, 1975 to W. F. McCarthy et al. The Abstract of U.S. Pat. No. 3,913,021 reads as follows: